Examples of self lubricating bearings are illustrated in the U.S. Daykin et al. Pat. No. 2,964,363, the U.S. Haller et al. Pat. No. 2,698,774; the U.S. Whiteley Pat. No. 2,048,763; the U.S. Farr Pat. No. 1,156,071; the U.S. Chalmers Pat. No. 983,025; the U.S. Whiteley Pat. No. 2,067,034; and the U.S. Love Pat. No. 2,710,236.
Attention is also directed to the U.S. Gits Pat. No. 3,013,762; the U.S. Eudier Pat. No. 3,352,612; and French Pat. No. 794,098.
As is illustrated in those patents, it is known to utilize lubricant filled reservoirs on or communicating with the sliding surfaces of self-lubricating bushings and bearings wherein the reservoirs are supplied with lubricant prior to the assembly of the structure and wherein the lubricant is distributed between the sliding surfaces through frictional contact of one of the moving surfaces with the surface of the lubricant disposed in the reservoirs. Such rigid type bushings having prelubricated reservoirs suffer a disadvantage in possible depletion of a portion of the lubricant contained in the reservoirs through absorption in the bearing structure, expulsion from the system, or evaporation which decreases the effectiveness of lubrication since the lubricant gradually recedes from contact with the moving surfaces as its volume is diminished. Devices of the prior art have attempted to overcome this disadvantage by providing reservoir systems which route the lubricant discharged from the reservoirs by centrifugal force, back to the reservoirs thereby providing a recovery and replentishing circuit for the bushing. A disadvantage here lies in the complexity required to achieve this recirculation and also the necessity of a relatively high rotational speed to accomplish the recirculation effect. This solution is unsuitable in lower speed application where centrifugal forces are not present.